A multispectral image includes image data at specific frequencies within a given frequency spectrum. One example of a multispectral image is a color image including image data for the red, blue, and green colors within the visible spectrum. Multispectral image systems, such as digital color imagers used in smartphones and digital cameras, can be used to capture multispectral images. A typical multispectral image system includes a pixel array for sensing the intensity of incoming light and a filter array for limiting the light hitting an individual pixel to a given frequency range. For example, a digital camera includes a color filter array having three color filter elements.
The most common configuration of the color filter array is the Bayer filter mosaic where three color filter elements are arranged in groups of four as 2×2 grids across the array. Each color filter element transmits light of one color and absorbs light outside the selected color spectrum. Within the group of four filter elements, one filter element transmits red light, one transmits blue light, and two transmit green light. Thus, only about 50% of the green light, 25% of the blue light, and 25% of the red light make it through the filter and can contribute to the signal reaching the pixel.
Further, the trend in imagers is for the imager to be smaller and provide higher resolution. As a result, the pixels in the pixel array continue to shrink, and their low-light performance continues to degrade due to low light transmission and relatively higher pixel noise. Thus, there is a need for a multispectral imager that can transmit more light through its filter array to improve its low-light sensitivity.